The invention relates generally to access to data stored in computer systems, and deals more particularly with managing video data stored on disk to supply video-on-demand application.
Currently, "pay-per-view" movies are available via "Cable Television". The Cable Television supplier makes the pay-per-view movies available at pre-determined times, and subscribers can register to view the movie at the pre-determined times. At those times, the Cable Television supplier transmits the movie via the normal television cable on a special channel reserved for the pay-per-view movies. All subscribers of the pay-per-view movie receive the movie at the same time on the same channel. While this is an effective way to supply a movie to subscribers, many subscribers do not want to be limited as to viewing times; they want to view the movie at a time of their choice.
"Video-on-demand" refers to the furnishing of a video movie to viewers via a computer network at times selected by each viewer and under the control of the viewer. One or more copies of the movie are stored, each on a separate direct access storage device (DASD) such as disk. Upon request by the viewer, the viewer is granted access to a copy of the movie and can begin to read the movie. A pointer tracks the progress of the viewer.
There is a limit to the number of viewers that can be supplied from each disk. This limit is based on the bandwidth available for reading the movie from the disk to a server and the bandwidth available for transmitting the movie from the server to the viewer. Usually, the bandwidth available for the server to access the disk is the limiting factor as a single disk is typically used to supply ten to twenty viewers. The bandwidth available for accessing the disk is limited by the mechanical motion required by a disk read head and the disk itself.
Each copy of a typical video movie requires a large amount of disk storage and this storage is expensive to provide. Consequently, it is desirable to minimize the number of copies yet accommodate viewer requests and do so promptly. At the start of service, enough copies of the movie are made on different disks and enough bandwidth is reserved on these disks to satisfy an expected number of concurrent viewers. It was known for an operator to track the number of viewers of each movie. When the number of current viewers increases to a pre-determined percentage of the total expected number, then the operator may request that additional bandwidth be reserved on the disk(s) that already contain copies of the movie, provided that additional bandwidth is available, or that another copy be made on another disk.
European Patent Application 95102075.9, Publication Number 0 683 464 A2 discloses a video-on-demand system. There are multiple copies of the same movie on different disks, and each disk contains copies of different movies. The computer system monitors the number of video movies being read concurrently from each disk and balances the loads on the disks by transferring the reading of a movie from an overloaded disk to another, underloaded disk containing a copy of the same movie. The computer system also periodically transfers movies between the disks to optimize load balancing based on the user performance requests for each of the video movies.
A general object of the present invention is to provide a video-on-demand system which automatically tailors the number of copies of movies and allocated bandwidths to viewer requirements.
Another general object of the present invention is to provide a video-on-demand system of the foregoing type which promptly provides requesters with access to movies.